Investigation of interactions between zein and natamycin by fluorescence spectroscopy and molecular dynamics simulation

Abstract

Zein nanoparticles have been demonstrated as an efficient nanocarrier for natamycin to improve its solubility and stability. This study investigated the molecular-level interactions between the complex of zein with natamycin. The fluorescence properties including excitation-emission spectra and fluorescence lifetime of zein were first determined. The fluorescence quenching of zein by natamycin was analyzed by Stern-Volmer equation and was static with a rate constant Kq of 0.633 × 1013 M−1 s−1 at 303 K. The association constant (Ka) at different temperatures were calculated in order to obtain thermodynamic process parameters. The quenching process was spontaneous with a binding constant Ka of 1.134 × 105 M−1 at 303 K. The positive sign of ΔH and ΔS indicates that the hydrophobic interactions play a major role in the formation of the zein-natamycin complex. The interaction mechanisms between zein and natamycin were further studied using molecular dynamics simulation. The geometrical figurations of the most possible binding model that stabilized by both hydrophobic interaction and hydrogen-bond network were presented. The complex was formed with both hydrophobic interactions between the conjugated tetraene group of natamycin and the Phe (183), Val (184), Leu (181) and Phe (123) residues of zein, and hydrogen-bonds network between the OH groups of natamycin and the Val (18), Gln (116), and Ser (112) residues of zein.